Process for preparing organopolysiloxanes

Abstract

A targeted molecular weight of an organopolysiloxane is obtained in a two stage hydrolysis by hydrolyzing a chlorosilane with from 0.002 to 0.6 mol of water in a first step in the presence of alcohol, in which the pressure and/or temperature are adjusted such that following further hydrolysis in a second step, the targeted molecular weight is obtained.

The invention claimed is: 
     
       1. A process for the production of an organopolysiloxane of a targeted molecular weight, comprising:
 providing a continuous, two-stage reactor for the preparation of the organopolysiloxane, and in the reactor 
 a) in a first step, continuously reacting one or more chlorosilanes with from 0.002 to 0.6 mol of water per mole of hydrolyzable chlorine and 0.3 to 1.6 mol alcohol per mole of hydrolyzable chlorine at a temperature and a pressure, such that gaseous hydrogen chloride is evolved, to produce a partial hydrolysate, 
 b) in a second step, optionally mixing the partial hydrolysate with a water-insoluble organic solvent having a density of less than 0.9 g/ml, and metering in water in an amount of from 0.2 to 100 mol per mole of hydrolyzable chlorine in the chlorosilane(s); and 
 c) in a third step, separating an aqueous alcoholic phase from a phase containing the organopolysiloxane product of said targeted molecular weight; 
 the process further comprising first preparing a first organopolysiloxane having a first molecular weight in the reactor by the above steps, and measuring the molecular weight of the first organopolysiloxane; and 
 comparing the first molecular weight to the targeted molecular weight and if the first molecular weight is not the targeted molecular weight, regulating the molecular weight of an organopolysiloxane product later isolated to the target molecular weight by adjusting at least one of the temperature and pressure, an increased pressure elevating the molecular weight and an increased temperature lowering the molecular weight. 
 
     
     
       2. The process of  claim 1 , wherein, in the first step, chlorosilanes are reacted with from 0.0021 to 0.58 mol of water per mole of hydrolyzable chlorine. 
     
     
       3. The process of  claim 1 , wherein, in the first step, chlorosilanes are reacted with from 0.35 to 1.5 mol of alcohol per mole of hydrolyzable chlorine. 
     
     
       4. The process of  claim 2 , wherein, in the first step, chlorosilanes are reacted with from 0.35 to 1.5 mol of alcohol per mole of hydrolyzable chlorine. 
     
     
       5. The process of  claim 1 , wherein, in the first step, the molar water-to-alcohol ratio used is from 0.0015 to 1.45. 
     
     
       6. The process of  claim 2 , wherein, in the first step, the molar water-to-alcohol ratio used is from 0.0015 to 1.45. 
     
     
       7. The process of  claim 3 , wherein, in the first step, the molar water-to-alcohol ratio used is from 0.0015 to 1.45. 
     
     
       8. The process of  claim 4 , wherein, in the first step, the molar water-to-alcohol ratio used is from 0.0015 to 1.45. 
     
     
       9. The process of  claim 1 , wherein, in the second step, a water-insoluble solvent is added. 
     
     
       10. The process of  claim 2 , wherein, in the second step, a water-insoluble organic solvent is added. 
     
     
       11. The process of  claim 3 , wherein, in the second step, a water-insoluble organic solvent is added. 
     
     
       12. The process of  claim 4 , wherein, in the second step, a water-insoluble organic solvent is added. 
     
     
       13. The process of  claim 5 , wherein, in the second step, a water-insoluble organic solvent is added. 
     
     
       14. The process of  claim 6 , wherein, in the second step, a water-insoluble organic solvent is added. 
     
     
       15. The process of  claim 7 , wherein, in the second step, a water-insoluble organic solvent is added. 
     
     
       16. The process of  claim 8 , wherein, in the second step, a water-insoluble organic solvent is added. 
     
     
       17. The process of  claim 1  wherein the pressure in the first step is regulated by adjusting the take-off pressure of the hydrogen chloride gas liberated in the first step. 
     
     
       18. The process of  claim 1 , wherein all the chlorosilanes are methylchlorosilanes and the organosiloxane product is a linear or branched organopolysiloxane. 
     
     
       19. The process of  claim 1 , wherein the organopolysiloxane product is a solid organopolysiloxane resin. 
     
     
       20. The process of  claim 1 , wherein no water-insoluble organic solvent is present in the first step.